Batteries

Batteries store electricity for use at a later time when a charging source (sun, wind, water or generator) is not available. They also provide a reserve of available energy to run loads that require more power than that provided by the charging source.

Batteries are also one of the most misunderstood components of alternative energy system. I will attempt to dispel a few myths:

"Deep Cycle" is a term used far to often in the wrong situation. Batteries that are sold as marine/RV deep cycle - in the 24 and 27 series are no more than slightly modified starting batteries with a different label. We speak to clients on a daily basis who purchase these batteries at a discount retailer, or have been told these are the proper batteries for the application, only to find out a year later they battery requires replacement. These batteries, as well as any car type starting batteries, including 4D and 8D starting batteries are simply not suitable for alternative energy applications and will yield unsatisfactory performance.

A true deep cycle battery, such as a golf cart of forklift batteries are designed from the ground up for deep cycling applications. This does not mean, however, you should completely discharge the batteries on a regular basis! Any battery which is rated in cold cranking amps is not a deep cycle.

Cycling - The deeper you discharge a lead-acid battery, the shorter it's lifespan. Period. Small batteries (NiCad) for consumer goods and electronics have completely different charging characteristics, and actually require full discharges to maintain their capacity. A battery bank should be sized for no more than a 50% discharge on a regular basis. If it gets discharged deeper than that occasionally, that's life, but you should not always discharge your batteries until they will no longer operate.

Used batteries - There are many people who report getting "great deals" on old phone company batteries, or standby UPS batteries. There are risks associated with purchase of any used gear. If you are able to do proper load testing on a bank of batteries you are purchasing, it will tell you exactly what condition they are in. Relying simply on their age or the reported usage will not tell you the condition they are really in. Be cautious! You could end up with 2000 lbs of batteries that are no good and then you must often pay to have them disposed of properly.

More information on batteries

Battery University. All the information you ever want to know about batteries.